A network router is a critical device in networking that connects multiple networks and directs data packets between them. It plays a key role in ensuring efficient communication between devices on different networks, including the internet.
In this lesson, we will cover:
What is a Router?
Router Functions
Types of Routers
Routing Tables and Protocols
Configuring a Router (Practical)
Troubleshooting Routers
1. What is a Router?
A routeris a device that forwards data packets between networks. It operates at Layer 3 (Network Layer) of the OSI model and determines the best path for data to travel.
Example:
When you visit www.google.com, your home router forwards your request to the ISP, which then routes it to Google’s servers.
Key Components of a Router:
CPU (Processor): Handles data processing.
Memory (RAM, ROM, Flash, NVRAM): Stores configuration and temporary data.
Interfaces (Ports): Ethernet ports for connecting devices.
Routing Table: Maintains network paths.
2. Router Functions
A router performs several key functions:
2.1 Packet Forwarding
Uses the routing table to determine the best path.
Works with IP addresses (not MAC addresses like switches).
2.2 Network Address Translation (NAT)
Allows multiple devices in a private network to share a single public IP.
Essential for home and enterprise networks.
2.3 Dynamic Host Configuration Protocol (DHCP)
Assigns IP addresses dynamically to devices.
2.4 Firewall and Security
Some routers have firewall features to block malicious traffic.
2.5 Quality of Service (QoS)
Prioritizes certain types of network traffic (e.g., VoIP over regular browsing).
3. Types of Routers
Routers can be classified based on their usage:
3.1 Wired Routers
Connect to a network via Ethernet cables.
Example: Cisco enterprise routers.
3.2 Wireless Routers
Provide Wi-Fi connectivity.
Common in homes and offices (e.g., TP-Link, Netgear).
3.3 Core Routers
High-performance routers used in large networks (e.g., ISPs).
3.4 Edge Routers
Connect internal networks to external networks (like ISPs).
3.5 Virtual Routers
Software-based routers (e.g., used in cloud networking).
4. Routing Tables and Protocols
A router makes forwarding decisions based on the routing table and routing protocols.
Topology
4.1 Routing Table
A routing table contains:
Destination Network: The target network.
Next Hop: The next router to forward the packet.
Metric: The cost of the path.
Example of a Routing Table (Cisco CLI Output)
4.2 Routing Protocols
Routing protocols help routers exchange information and update their tables.
Types of Routing:
Static Routing: Manually configured routes.
Dynamic Routing: Uses protocols to update routes automatically.
Common Routing Protocols:
RIP (Routing Information Protocol) – Uses hop count.
OSPF (Open Shortest Path First) – Uses link state.
BGP (Border Gateway Protocol) – Used on the internet.
5. Configuring a Router (Practical)
5.1 Setting Up a Cisco Router (Basic Configuration)
We will configure a Cisco router using Packet Tracer or a real router.
Step 1: Connect to the Router
Use a console cable and connect it to a PC.
Open PuTTY or Tera Term to access the router’s CLI.
Step 2: Enter Privileged Mode
Step 3: Set a Hostname
Step 4: Configure an Interface (Assign IP Address)
Step 5: Configure Routing (Static Route Example)
Step 6: Save Configuration
6. Troubleshooting Routers
6.1 Checking Connectivity
Use ping to test connectivity.
6.2 Viewing the Routing Table
6.3 Checking Interface Status
Conclusion
A router directs network traffic and connects multiple networks.
Uses routing tables and protocols (Static, OSPF, RIP, BGP, etc.).
Can be configured using CLI(Cisco routers).
Troubleshooting involves checking routes, interfaces, and logs.
R1#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
10.0.0.0/30 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, Serial0/0/0
C 192.168.1.0/24 is directly connected, FastEthernet0/0
S 192.168.2.0/24 is directly connected, Serial0/0/0
R1#
Router> enable
Router# configure terminal
Router(config)# hostname R1
R1(config)# h
R1(config)# interface FastEthernet0/0
R1(config-if)# ip address 192.168.1.1 255.255.255.0
R1(config-if)# no shutdown
R1(config)# ip route 192.168.1.0 255.255.255.0 10.0.0.2
R1# write memory
R1#ping 192.168.1.100
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.100, timeout is 2 seconds:
!!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 0/0/1 ms
R1#ping 192.168.2.100
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.2.100, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 6/11/18 ms
R1#
R1#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
10.0.0.0/30 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, Serial0/0/0
C 192.168.1.0/24 is directly connected, FastEthernet0/0
S 192.168.2.0/24 is directly connected, Serial0/0/0
R1#
R1#show ip interface brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 192.168.1.1 YES manual up up
FastEthernet0/1 unassigned YES unset administratively down down
Serial0/0/0 10.0.0.1 YES manual up up
Vlan1 unassigned YES unset administratively down down
R1#
